The systems, built on the basis of simple detectors (U.S. Pat. No. 4,001,771, issued on Jan. 4, 1977, G08B 13/00), which contain one or several seismic sensors, analog-to-digital converters and digital processing module are known. These detectors calculate the power of the seismic signal and, if the power value exceeds the preset threshold, recognize the seismic event at the distance LMAX—maximum distance between the detector and the seismic disturbance source, at which the disturbance signal is recognized by the detector as a seismic event. The chain of such detectors forms a security system.
Disadvantage of this kind of the systems is that detectors do not determine the direction to disturbance source, therefore it is impossible to identify, where the event took place—within the protected zone or beyond its boundaries. Only to localize the disturbance source, inside or outside of the security zone, it is necessary to install two parallel chains of detectors at the distance of about LMAX. A double number of detectors and connecting cables and double labor costs for installation of the system are thus required.
The system (application WO2010090752, publication of Aug. 12, 2010, H04B 1/06), enabling to identify that the disturbance source is underground, is also known. For this purpose, one of the sensors is installed close to the surface, and the second is installed at a greater depth. The processing method requires the upper sensor to recognize the surface wave, and the lower one mainly the volume wave.
Disadvantage of the system shortage is that, to ensure the functioning of the system, the lower sensor is buried at a depth of about 3-6 m, which makes the installation work much more expensive. In the vertical direction, this detector recognizes only two values ‘underground’-‘surface’, but it doesn't determine the direction to the underground disturbance source.
The closest engineering solution to the disclosed invention is the security system detector (U.S. Pat. No. 7,202,797, publication Apr. 10, 2007, G08b 21/00) for protection of an extended facility, e.g. a pipeline. The system consists of a set of detectors. Each detector consists of several seismic sensors installed sequentially in a line at a short distance to each other (1-3), and this line is perpendicular to the protected pipeline. Outputs of the sensors are connected to the analogue-to-digital converters of the digital processor. Each detector determines the phase shift for each pair of sensors and, based on the phase shift, the direction of the disturbance source. The evaluation of the corresponding angle demands the knowledge of the seismic wave velocity. The velocity is a variable value, therefore the detector is equipped with an active disturbance source, and the velocity of the seismic wave is calculated at its periodic activation.
Disadvantage of the said device is the presence of additional technical means for generation of the reference seismic disturbance and measurement of the velocity of the seismic wave from this disturbance. Another disadvantage of the device is that it doesn't determine the direction to the underground seismic disturbance source.